Located on the Arabian Peninsula, the Arabian Desert and East Sahero-Arabian Xeric Shrublands , and extending north to surround the Dead Sea, is a desert ecoregion, one of the most vast continuous bodies of sand on Earth. The ecoregion is classified within the Deserts and Xeric Shrublands biome. Given the aridity of this habitat, there is an impressive faunal biodiversity, with 507 vertebrate species having been recorded here.

This ecoregion holds little floral biodiversity, although a few endemic plants occur here. Many faunal species, such as the Striped Hyaena, Jackal, and Honey Badger have become extirpated in this area due to hunting, human encroachment, and habitat destruction. Certain other species have been successfully re-introduced, such as the endangered Arabian Oryx and the Sand Gazelle, and are protected at a number of reserves. Overgrazing by livestock, off-road driving, and human destruction of habitat are the chief threats to this desert ecoregion.

Location and general depiction

Arabian Desert and East Sahero-Arabian xeric shrublands
This is the largest ecoregion of the Arabian Peninsula, stretching from the Yemeni border to the Arabian Gulf and from Oman to Jordan and Iraq. Within this area lies a vast wilderness of sand, ‘a desert within a desert so enormous and desolate that even the Arab peoples term it the Rub’al-Khali or the Empty Quarter. It is arguably the most extensive continuous body of sand anywhere on Earth, with a land area of over 500,000 square kilometres (km2), or about the size of France. Egypt’s Sinai Desert and Israel's Negev Desert lie within this ecoretion, as well as much of southern and eastern Jordan, western Iraq, and northern Saudi Arabia. Bordering the Arabian Gulf, there is an extension into Qatar and, further east, the region covers almost all of Abu Dhabi in the United Arab Emirates (UAE). The Rub’al-Khali crosses over from Saudi Arabia into western Oman and eastern Yemen.

Geology

Negev Desert viewed from the ancient Masada site. The Dead Sea is in the distance. @ C.Michael Hogan
Three distinctive physical features are evident in this vast desert territory. A biological corridor of sandy terrain known as the ad-Dahna Desert connects the large an-Nafud Desert (approximately 65,000 km2) in the north of Saudi Arabia to the Rub’al-Khali in the south. Cutting through this corridor is the Tuwayq escarpment, an 800-kilometre (km) arc of spectacular limestone cliffs, plateaus, and canyons with fantastic shapes etched by the wind and sand on the high cliffs. The Wahiba sands of Oman form an isolated sand sea bordering the east coast and appear as a remarkable feature on any satellite image of the area.

The Rub’ al-Khali deserves further attention due to its dominant position in this ecoregion. It is a sedimentary basin elongated on a southwest to northeast axis across the Arabian shelf. Its surface elevation in the far southwest is 800 metres (m), declining rather steadily over a distance of 100 km to nearly sea level in the northeast. The sand overlies gravel or gypsum plains and can vary in depth from zero to 250 m, whereas in the eastern margins the dunes reach maximum heights of up to 250 m. Dune types range from solitary barchan dunes to extensive longitudinal dunes (300 km long) in the southwest and colossal dune mountains in the northeast. The sands are predominantly silicates, composed of 80 to 90 percent quartz and the remainder feldspar, whose iron oxide-coated grains give the sands a strong orange-reddish colour. The natural beauty of the sand desert is striking with its reddish dunes, sculptured by the wind, and stretching as far as the eye can see to the horizon.

Brackish salt flats exist in some areas, the most famous being the quicksands of Umm al Samim. A traveling companion of Wilfred Thesiger told of a raiding party perishing in the quicksands and how a entire herd of goats disappeared beneath the soil surface.

Climate

Much of the Rub’al-Khali is classified as ‘hyper-arid’, where more than twelve consecutive rain-free months have been recorded in an area that lacks seasonal precipitation. Rainfall is generally less than 35 millimetres (mm) per annum, and daily mean relative humidity is about 52 percent in January and fifteen percent in the June-July period. Daily maximum temperatures average 47°C in July and August, reaching peaks of 51°C.

The daily minimum average is 12°C in January and February, although frosts have been recorded. Daily extremes of temperature are considerable. Saudi Arabia’s northern Harrat al Harrah Nature Reserve is subject to hot summer temperatures, averaging 27.8°C, and very cold winters averaging 6.8°C, with frost common in mid-winter and an average rainfall of less than 80 millimetres.

Biota

The Rub’al-Kali is notable for its very limited floristic diversity. There are only 37 species, of which about 20 have been recorded from the main body of the sands, and 17 mostly dwell around the outer margins; of these, one or two are endemic species. Vegetation may be described as very diffuse, but fairly evenly distributed sand shrubland, interrupted in some parts by near sterile inter-dune floors. Typical plants present are Calligonum crinitum on dune slopes and tussocks of sedge (Cyperus conglomeratus). Other widespread associates are Dipterygium glaucum, Limeum arabicum, and Zygophyllum mandavillei. Trees are generally absent, except around the outer margins, and are typically the Desert Acacia (Acacia ehrenbergiana) andJand (Prosopis cineraria) in drainage lines and pans between dunes. Along the northern edge of the Rub' al-Khali sands in the UAE, Calligonum comosum is the characteristic woody perennial, growing in wind-blown sand, with a succession of annual herbs that thrive after desert rain. There are a number of special status taxa that are found in the Arabian Desert and East Sahero-Arabian xeric shrublands, denoted by the increasing threat gradations of Lower Risk (LR), Near Threatened (NT), Vulnerable (VU), Endangered (EN), or Critically Endangered (CR).

Biodiversity characteristics

Unique to Oman’s Wahiba sands are the expanses of single species ghaf (Prosopis cineraria) woodlands, which can be up to 85 kilometres in length and 20 kilometres wide. These woodlands provide vital shade and nesting habitat for birds. The sands here are also thought to act as a major ecological barrier dividing the faunal species of the northern mountains from those of central and southern Oman. The best example is the division between the Arabian Tahr (Hemitragus jayakari EN), which occurs in the northern mountains but not south of the Wahiba, and the Nubian Ibex (Capra nubiana), which does occur south of the Wahiba, but is in turn absent from the northern mountains.

Mammalian detail

Nubian Ibex males, Judaean Desert. @ C. Michael Hogan
The Arabian Jird (Meriones arimalius) is an endemicmammal found in the ecoregion. In Saudi Arabia, gazelle and oryx have been successfully re-introduced after motorized hunting parties had virtually exterminated them by the early 1970’s. At the Uruq Bani Ma’arid protected area, Arabian Oryx (Oryx leucoryx EN) again roam the sands, as do Goitered Gazelle (Gazella subgutturosa) and Mountain Gazelle (G. gazella VU).

Avian detail

Greater Flamingo (Phoenicopterus ruber) caused a stir when they bred in Abu Dhabi in 1993, representing the first documented occasion in Arabia since 1922. The rare Houbara Bustard (Chlamydotis undulata VU) also inhabits this ecoregion. The Basra Reed Warbler (Acrocephalus griseldis EN), a species severely impacted by the Iraqi marsh drainages by the Saddam Hussein regime in the late 20th century, can be found in the ecoregion

Reptilian detail

There are four fringe fingered lizards endemic to the Arabian Desert and East Sahero-Arabian xeric shrublands: Haas' Fringe-fingered Lizard (Acanthodactylus haasi); Be’er Sheva Fringe-fingered Lizard (Acanthodactylus beershebensis CR); Saudi Fringe-fingered Lizard (Acanthodactylus gongrorhynchatus), found only in eastern Saudi Arabia and western United Arab Emirates ; and the Long Fringe-fingered Lizard (Acanthodactylus longipes), a sexually dimorphic taxon found in soft sand habitats. The Egyptian Tortoise (Testudo kleinmanni CR) is a special status reptile found in shallow sandy wadis and coastal marshes of the ecoregion; the Euphrates Softshell (Rafetus euphraticus EN) is found in the ecoregion and threatened by water pollution. The rare Omani Spiny Tailed Lizard (Uromastyx thomasi) can also be found in the Arabian Desert and East Sahero-Arabian xeric shrublands.

Amphibian detail

Only a few amphibian taxa are found in the ecoregion. The Arabian Toad (Bufo arabicus) is a near endemic, occurring only on the Arabian Peninsula. Also found in the Arabian Desert and East Sahero-Arabian xeric shrublands is the European Green Toad (Pseudepidalea viridis).

Vegetative detail

An amazing sight following heavy rain is the new vegetation that appears, as the seeds of annuals that have lain dormant explode into a carpet of flowers. Other life forms triggered by rainfall include the fascinating ‘instant crustacean’ (Triops); this creature lies dormant for years until the arrival of a rainstorm and then hatches, moults from its cyst, and grows to its full size within the span of several days.

Ecological status

Over the last few decades the desert of the UAE has witnessed local extirpations of Canis lupus arabs, Oryx leucoryx, Hyaena hyaena, Jackal (Canis aureus), and Honey Badger (Mellivora capensis). Gazelle subgutturosa and G. gazella still survive, though with very small populations and restricted ranges. The Sand Cat (Felis margarita), Ruppell's Fox (Vulpes rueppellii) and Cape Hare (Lepus capensis) are thought to be far less numerous than they were.

In Saudi Arabia, a comprehensive network of protected areas covers many key sites, based on a system plan. These areas are managed by the National Commission for Wildlife Conservation and Development (NCWCD), assisted by its two prominent research centres, the King Khalid Wildlife Research Centre (KKWRC) and the National Wildlife Research Centre (NWRC) in Taif. The stony basaltic desert of Harrat al Harrah, whose northern boundary borders Jordan and Iraq, was established in 1987 as Saudi Arabia’s first national reserve (12,150 km2). The landscape is dominated by numerous uplifted extinct volcanic cones and black basaltic boulders of the middle Miocene, making vehicle access generally impossible. The reserve provides habitat to over 250 species of plants, 50 species of birds and 22 species of mammals.

The Uruq Bani Ma’arid is a 12,000km2 reserve on the western edge of the Rub’ al-Khali. Projects to re-introduce Oryx leucoryx and Gazelle subgutturosa began here in 1995. The NCWCD established the Ibex Reserve (200 km2) south of Riyadh to protect Capra ibex nubiana which, in 1994, numbered c. 259. This reserve also serves as a re-introduction site for Gazelle gazella which, by 1994, numbered c. 160. The At-Tabayq Special Nature Reserve in northern Saudi Arabia is also a protected area for Capra ibex nubiana.

In Jordan, the Royal Society for the Conservation of Nature (RSCN) is the body responsible for the creation and management of protected areas. Within this ecoregion, the Shaumari Wildlife Reserve protects vegetation, Gazelle spp., and the re-introduced onager (Equus hemionus). In 1978, this reserve was one of the first re-introduction sites in the Arabian Peninsula for Oryx leucoryx. In southern Jordan, the RSCN is working to establish a Wadi Rum Nature Reserve.

Ecological threat profile

Common threats to biodiversity in this ecoregion are wildlife poaching, overgrazing, and damage to vegetation caused by off-road driving. In Egypt, additional threats are being posed by a set of military and revolutionary actions beginning in the so-termed Arab Spring.

A number of threats face UAE’s desert environment, including overgrazing by camels and goats, damage to vegetation through off-road driving, and habitat disturbance and fragmentation in the form of roads, agricultural projects and oil and gas surveys. No formal protected areas exist at the time of writing but a number of protected areas are in the planning for Abu Dhabi.

Hatough-Bouran & Disi describe how flora and fauna in the eastern deserts of Jordan are threatened by overgrazing. Socio-economic changes involving livestock subsidies and the introduction of water tankers have resulted in increased herd sizes and a more sedentary lifestyle amongst the Bedu. Similar overgrazing problems are reported for Saudi Arabia by Thouless et al., and such pressures are common elsewhere in this ecoregion.

Justification of ecoregion delineation

This ecoregion boundary was formed using Zohary’s geobotanical map of the Middle East. It corresponds to Zohary’s classified regions of Saharo-Arabian desert vegetation of Anabasetea articulatae and Sahara-Arabian interior sand desert vegetation of Haloxylo-Retametalia raetami (including Haloxylion persici arabicum).

References

S. Aspinall. 1996. Status and conservation of the breeding birds of the United Arab Emirates. Hobby, Liverpool and Dubai. ISBN: 1900724138

K. Brown. 1988. Ecophysiology of Prosopis cineraria in the Wahiba Sands, with reference to its reafforestation potential in Oman. Journal of Oman Studies, Special Report 3:257-270.

G. Child and J. Grainger. 1990. A system plan for protected areas for wildlife conservation and sustainable rural development in Saudi Arabia. National Commission for Wildlife Conservation and Development, Riyadh, Saudi Arabia.

This article contains some information that was originally published by the World Wildlife Fund. Topic editors and authors for the Encyclopedia of Earth have edited its content and added substantial new information. The use of information from the World Wildlife Fund should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content